1. Field of the Invention
The invention relates to an image processing device, an image processing method, and an image processing program storage medium, and particularly relates to: an image processing device in which correction is performed to an image obtained by reading out, as a current, charge from a radiographic image detector in which the charge which is formed by converting irradiated radiation is accumulated and stored; to an image processing method applicable to the image processing device; and to a storage medium storing an image processing program to cause a computer to function as the image processing device.
2. Description of the Related Art
Systems that obtain digital radiographs are known in radiography for medical diagnostic purposes. In these systems, radiation passing through the image target is irradiated onto a radiographic image detector provided with a photoelectric conversion layer sensitive to radiation, charges that are accumulated in the radiographic image detector according to the amount of radiation irradiated on the radiographic image detector are sequentially read out as current for each unit region for reading out, and the read-out current is converted into digital data. In such a radiographic image detector, when charge is read out from a given unit region, leakage current may occur from the unit regions with charge that is yet to be read out, with this leakage current being superimposed on the current being read out and leading to a deterioration in the image quality of the read-out image.
To address this issue, Japanese Patent Application Laid-Open (JP-A) No. 2006-304213 discloses a technique for obtaining an image with the influence of leakage current removed therefrom. In this technique, unit regions with condensers for accumulating charge converted in an X-ray conversion layer, and with thin film transistors (TFTs), for reading out the charge accumulated in the condensers by switching of on/off, are two-dimensionally arrayed, and plural gate lines and plural signal lines are also two-dimensionally arrayed. In such a configuration, after charge has been read out from all of the unit regions, a value as the leakage current when reading out the charge of a particular unit region, is derived by summing up all of the signal levels for each unit region that is connected to the same data line as the particular unit region and whose charge is unread when the particular unit region is read out, and multiplying coefficient A by the summed value. The signal level of the particular unit region is corrected according to the derived leakage current values, and an image removed of the influence of leakage current is obtained by carrying out such correction to all of the unit regions.
However, it is found apparent from the investigations carried out by the inventor of the present application that the leakage current from individual regions in the radiographic image detector attenuate with time (details of these investigations are given below). However, the above technology does not consider the above changes in the leakage current due to attenuation with time, and the precision of correction for leakage current influence is insufficient.